Detonation nanodiamond (ND) is one of only a few nanomaterials that can be produced on an industrial scale. Unfortunately, the high content of non-diamond species in the detonation soot (e.g., amorphous and graphitic carbon, metal and metal oxides) prohibits a direct use of the as-produced material in most applications, making the purification one of the most critical steps in ND production. The selection of proper purification conditions requires detailed knowledge of the composition of the powders and the nature of impurities contained within. The development of efficient purification methods, therefore, relies on the availability of suitable characterization methods able to assess and quantify the purity of ND powders. At this point in time, there exists no individual purification step able to remove all impurities present in ND powders. Studies reported in the literature suggest that a combination of acid and air purification currently yields the highest purity levels, while minimizing losses in the diamond phase. Although much progress has been made in the development of efficient and economical purification methods over recent years, several challenges remain. In the short run the most critical step towards widespread utilization of ND is the standardization of the purity assessment. A standardized evaluation of ND purity will then allow for a direct comparison of the effectiveness of existing purification methods in collaboration with process complexity and treatment cost.